What is an app?

Apps are small programs that perform a specific task. You’ll find apps for tying a Windsor knot, a lightsabre simulator as well as satnavs and spirit levels. Want to convert currency when abroad or keep your child entertained en route? There’s an app for that, too.

The apps you’re able to download and run depends on the operating system used by your smartphone. Each OS has its own app store, where you can browse for apps, read user reviews and then download the ones you want. Many apps are free although you will need to pay for some.

What is an operating system?

Operating systems manage your phone’s hardware and software, in the same way that Windows manages your PC.

There are several systems currently favoured by mobile manufacturers, including Android and Windows Phone. Some companies like Apple and BlackBerry prefer to use their own proprietary systems.

How can I boost my phones battery life?

Your phone’s display is the largest drain on power - the brighter your screen, the more energy is required to power the backlight. Turn this down and reduce the time it takes before your backlight times-out and switches off.

Turn off Wi-Fi and GPS when you’re not using them and if you’re only going to use your phone for calls and texts for a while then consider switching from 3G to GSM (this may be listed as 2G in the Settings menu).

Download apps to track what’s using your battery and then turn off (or uninstall) any particularly power hungry apps. Also reduce the frequency that your phone checks for emails or syncs with Facebook.

How fast is 4G?

EE, the only company currently offering 4G, claims it offers download speeds that are up to five times faster than 3G. However the actual speed you’ll get will depend on a number of factors such as the device you're using, the signal strength and the number of people on the network.

EE therefore reckons average 4G download speeds are likely to be between 8 and 10 megabits a second (Mbit/s), with possible instances of up to 40 Mbit/s. That’s similar to the most home broadband networks.

EE's 4G network offers much faster download speeds. Other operators will launch their own networks in the summer of 2013

How much data allowance do I need?

Almost all smartphone functions require an internet connection to work properly. For example, you’ll need data when browsing the web, sending e-mails, watching YouTube videos or updating Facebook and Twitter.

Most phones come with a data package, typically 500MB or 1GB each month. 500MB should be enough for most people as long as you’re not using your smartphone for data-intensive tasks such as downloading music or streaming videos.

It’s hard to say exactly what constitutes 500MB of data as every web page differs in size depending on the amount of text, images and other multimedia content it contains. However O2 estimates that 500MB is the equivalent of 1500 rich web pages (like bbc.co.uk), 5000 basic web pages (like Twitter), 1000 emails with photos attached or 60 short YouTube videos.

Check you have enough data to cover your usage - speak to your provider for more advice on the package which best suits your needs. And remember, your phone can consume data even when you’re not actively using it as it may be set up to run tasks in the background, such as checking for new emails or Facebook updates.

How can I stop myself running up a big bill?

Speak to your provider to ask if you can set a ‘cap’ or ‘limit’ on your account which will stop you spending over a certain level. Ask your provider how it works as some limitations may apply e.g. some caps might not cover you when you use your phone abroad.

Data is expensive so use local Wi-Fi instead of your phone’s mobile internet connection. Download an app to keep track of your usage and consider getting an app that can compress data as this will make your allowance go further.

If you let others use your phone, keep tabs on what they do. Avoid your child inadvertently racking up large bills from ‘in-app’ purchases by keeping your handset password private, or setting up a password.

If going abroad turn off data roaming (use Wi-Fi if you want to go online) and switch off your voicemail as you’ll have to pay to access it. Check what it will cost to use your phone and see if your provider offers special overseas packages. Alternatively consider buying an international Sim card or a local pay-as-you-go Sim card when you arrive at your destination. You’ll have to use a different number but will only pay local prices.

Protect your phone with a passcode and keep it safe when you’re out and about. Make a note of your IMEI number and phone provider’s contact details – you’ll need these to report your phone as lost or stolen while you are away.

Consider barring calls to premium rate services numbers to limit the usefulness of your phone to a thief.

I've been sent a huge bill after using my mobile phone abroad - do I have to pay?

Unfortunately, the answer is probably yes. There are rules in place about the cost of calls in EU countries and mobile providers are obliged to put a price cap on your usage to prevent you running up huge bills.

However, in countries outside the EU there's no protection, so providers can charge what they like. Legally they're not obliged to warn you if you're running up a big phone bill or to waive the charges if the bill is much higher than normal. However, it's worth asking your mobile provider to make an exception if you ran up a big bill because you were unaware of the costs.

What should I do if my phone is stolen?

Inform your network (or service provider) as soon as possible so it can bar your account. This will limit your liability for any further fraudulent calls made, but you'll still have to pay for any made before you notified them.

If you had previously noted down the handset's 15-digit IMEI number (accessed by typing *#06# into the phone, but sometimes found on the original packaging too), the network should be able to block that handset from working on any other UK network, rendering it worthless.

If you have mobile phone insurance, or the phone is covered under your house contents policy, check the terms and see if you're able to claim.

Is it illegal to unlock my phone?

No. Unlocking your phone is legal. However doing so may invalidate any handset warranty, so you may want to think twice if your handset is valuable.

It is illegal to attempt to make a stolen phone work by changing its IMEI code. If you suspect your handset is stolen then you need to report it to your service provider.

Can I keep my phone number if I switch provider?

Yes. Contact your old mobile phone provider and ask for your porting authorisation code (PAC). Many providers will supply this immediately over the phone, though some may ask you to request it in writing then send it to you by post.

Providers must send your PAC to you within two days of receiving your request (by phone or by post, depending on which method they use).

Give your PAC to your new provider, who will transfer your number over to your new service.

To see which networks came out on top in our customer satisfaction survey, read our best mobile networks advice guide.

Recycling specialists such as Mazuma Mobile will pay for your old mobile phone

I've upgraded to a new handset. What can I do with my old one?

To recycle your phone you can simply return your unwanted handset (minus the Sim card and any security or pin codes) to your network operator or phone retailer. The network will then usually make a donation to charity. Alternatively many charities run their own recycling schemes.

Another option is to sell your phone. Companies such as Mazuma Mobile and Envirofone will buy your old phone - all you do is enter your mobile phone's make and model on their website and they'll make you an offer for it. If you're happy with the price then the company will usually send you a pre-paid addressed envelope so that you can post the phone back to them.

Phone-buyers aren't the only solution if you want to sell your phone, although they're probably the easiest. Instead you can sell your handset privately, using online sites such as eBay or Gumtree. And some high street retailers, such as CEX, will allow you to trade in your old handset when you buy a new one while another option is to simply re-use the phone yourself.

If recycling or selling your phone ensure you erase any personal data stored on it. The easiest way of doing this is by resetting the phone’s factory settings.

If your contract has ended but the phone is in good condition then you can legally, and often freely, unlock it. This will let you use it on any network, allowing you to add a good value Sim card of your choice. These often offer great value for money.

Do mobile phones cause cancer?

Mobile phones, like all wireless devices that send and receive information, emit electromagnetic radiation which is not typically considered to be dangerous. All mobile phones sold in the UK must meet the requirements set by the government to limit the radiation that is absorbed by the body to 2W/kg. This is the device’s Specific Absorption Rate (SAR) which can be found on manufacturers’ websites.

Investigations have shown no evidence that radiation at these levels poses any short term health risks. The long-term effects are less well known as mobile phones have only been used for the last 15 years or so. Some studies have found slight indications of increased risks of some cancers, but these studies are far from conclusive. Organisations who are still wary of the risks have released precautionary advice which includes using hands-free kits to place the phone further from the body, using phones with a low SAR, making shorter phone calls and discouraging children from using phones.

Which? believes that mobile phones do not pose any short term health risks due to the radiation that they emit. Although there is no strong evidence to suggest any long-term effects, these risks are more uncertain, and we agree that further investigations may help to clarify this.